There is room for Improvement regarding the exposure. One the one hand, we se overexposed parts as well as deeply black part. The dynamic range of a Canon 5D Mark II brings better results. You can achieve better results by positioning your flashes correctly and regulate the strength manually. Further there's a colour cast, enhanced by oversaturating. A proper White Balance can help a lot. I hope you take your pictures in Raw format, so you can adjust WB manually as a first step of postprocessing. The pic is missing clearness and the final crisp of sharpness. Also two steps in postprocessing pictures.

Two steps of postprocessing? They are the first two steps, and they're always hard Most probably you can shot in RAW and JPEG Mode with your 5D, so you get a calculated version and one you can experience with. You'll see, soon your not satisfied anymore with the JPEG

Rule of thirds, fill the frame, there many ways to please the spectators. Often you can even combine them. In your pic its just a little shift to the left with your subject. At least the eyes are in the upper third! It doesn't matter, no, often it's mandatory to give the animals some space to breathe. (That's not an issue with this pic). As I stated in the critique: "frame nicely filled".

And sometimes, breaking the rule is the key to a perfect picture! But you have to know what you're doing.